Deleted PlayerRespawnTracker and removed all references to it - we
weren't going to use it anymore anyway. Renamed IDDoorLogic to IDimDoor
- abbreviating the "Dim" as D next to the standard I for Interface is
confusing. Renamed DDoorBase to BaseDimDoor and made it into an abstract
class - that's effectively what it was supposed to be. We should be
declaring methods as abstract rather than using empty ones. I renamed
the class because the convention for naming abstract classes is to start
the name with Base. Cleaned up code in other files.
